1. Field of the Invention
The present invention relates to a device for measurement of forces with a parallel spring arrangement. The invention is particularly suitable for the determination of forces and masses of small objects. The device in accordance with the invention can also be used for simultaneous measurement of surface profiles at several points.
2. Description of the Background Art
Various arrangements are known from the conventional art for force measurement or mass determination of objects and for measurement of surface profile deviations.
In numerous applications, bendable elements with strain gages applied to them are used for force measurement. For higher requirements in force measurement and weighing technology, deformation element parallel springs, for example made of aluminum, are used. Strain gages are likewise glued onto the surface of these deformation element parallel springs. Since the deformation element parallel springs exhibit both expansion and compression zones, the strain gages can be evaluated in full-bridge circuits. One drawback in this case is that the manufacturing of the strain gage force sensors requires a technologically intricate process. An additional drawback is the limited accuracy of these force sensors, especially for the measurement of small forces.
For determining the surface profiles of objects, silicon cantilevers in atomic force microscopes with resolutions in the nanometer and subnanometer range are used. The cantilevers used are silicon bending beams with piezoresistive resistances, which are connected into a bridge. Since these bending beam cantilevers have only positive or negative length expansions, full-bridge circuits cannot be realized. An ideal full-bridge circuit with piezoresistive resistances is only possible with a parallel spring arrangement.
It is also known to use cantilevers which have reflective surfaces at their free ends, the deflection of which is detected with flat-mirror interferometers. However, because of the inclination of the bending beam cantilevers at their free ends, flat-mirror interferometers can be used only at very small elongations and compressions.